The present invention relates to an electrode and associated capacitor structure for a semiconductor device, and more particularly to provision of a thin, oxygen-annealed, electrically conductive barrier layer adjacent a dielectric as part of the electrode.
A known capacitor includes two electrodes sandwiching a dielectric. A capacitance value of the capacitor characterizes an amount of charge that would be collected at the electrodes for a given applied voltage between the electrodes. This capacitance value is expressed by the equation
C=xcex5rxcex5oA/d
wherein
xcex5r=the relative dielectric constant of the dielectric between electrodes,
xcex5o=the permittivity of free space,
A=the surface area of the electrodes sandwiching the dielectric material, and
d=the distance between the electrodes.
The capacitance value (C) of the capacitor is directly proportional to an area (A) of opposing surfaces of the electrodes, directly proportional to a relative dielectric constant (xcex5r) of the dielectric, and inversely proportional to the distance (d) between the electrodes.
An ideal capacitor, once charged by a given applied voltage, would hold its collected charge for an infinite durationxe2x80x94i.e., permitting no leakage current through the dielectric between the electrodes. Such ideal capacitor would also tolerate large voltage applications. However, it is known that certain physical limitations of real-world materials restrict the availability of such an ideal capacitor.
Known dielectrics exhibit voltage breakdown characteristics, wherein the influence of a sufficiently large electric field causes a breakdown within the dielectric material. Accordingly, for a given voltage application, a minimum distance or dielectric thickness is maintained between electrodes in order to avoid short-circuit failures by way of the dielectric""s electric-field breakdown. Per the above equation, this requirement of a minimum distance between electrodes, therefore, limits the magnitude of the available capacitance value for a given electrode area.
Furthermore, known dielectrics currently are not capable of blocking all current leakage, but instead have a finite conductivity (i.e., less than infinite resistance) Thus a finite leakage current passes through the dielectric, which can deplete collected charge of the capacitor over a given period of time. As a result, when the capacitor is employed in a memory integrated circuit, e.g. a dynamic random access memory device, the capacitor requires a periodic refresh to restore the capacitor""s charge before it is depleted. Preferably low, The refresh frequency for a memory device is governed by the charge retention capabilities of the capacitor and the amount of charge that it is able to collectxe2x80x94which parameters/qualities, in turn, are proportional to the capacitance value of the capacitor and its applied voltage, respectively.
As inferred above, memory integrated circuits (e.g., a dynamic random access memory semiconductor devices) commonly employ capacitor elements. Manufacturers of these components continually push to shrink device geometries as a part of reducing manufacturing costs. However, given that the capacitance of a capacitor is directly proportional to the area of its electrode plates, a technical compromise exists between (i) the desire to reduce device geometry, and (ii) the need to maintain, or increase, charge retention of the capacitor for improving the performance of associated memory devices.
Embodiments of the present invention provide new electrode and capacitor structures, and methods of fabrication thereof, which overcome at least some of the above limitations and trade-offs.
In accordance with a first embodiment of the present invention, a capacitor structure comprises a dielectric layer sandwiched between first and second conductive layers. At least one of the first and second conductive layers includes a barrier portion formed to reduce migration of elements between the electrode and the dielectric. In accordance with one exemplary aspect of this embodiment, the barrier portion comprises oxygen-rich conductive material, and more preferably, oxygen-annealed refractory metal nitride adjacent the dielectric layer. More preferably, the refractory metal nitride of the barrier layer is of the group consisting of titanium nitride, tungsten nitride and tantalum nitride.
In accordance with one illustrative aspect of this first embodiment, the barrier layer comprises about 5 to 50 angstroms of oxygen annealed refractory metal nitride and the dielectric comprises tantalum pentoxide.
In accordance with a second embodiment of the present invention, an electrode structure overlays an oxide dielectric. The electrode structure comprises a layer of an oxygen-rich refractory metal nitride. Being oxygen-rich, the barrier layer is theorized to reduce migration of contaminants between the dielectric and the electrode. In accordance with one illustrative aspect of this second embodiment, the oxygen-annealed refractory metal nitride has a thickness of about 5 to 50 angstroms.
In accordance with a third embodiment of the present invention, a method of manufacturing a capacitor of a semiconductor device includes forming a first electrically conductive layer and a dielectric layer over a substrate. After forming the dielectric layer over the first electrically conductive layer, a thin layer of a conductive material is deposited over the dielectric. The thin layer of material is oxygen-annealed using an oxidizing gas of the group consisting of oxygen, ozone and nitrous oxide. Preferably, the oxygen-anneal is preformed in a process chamber which is the same as that used for depositing the barrier layer. In accordance with another aspect of this method of manufacturing, the oxygen-anneal comprises flowing oxidizing gases together with precursor gases of the conductive material during chemical vapor deposition thereof. In one exemplary embodiment, the conductive material comprises refractory metal nitride.
In a method of forming an electrode, in accordance with the present invention, a thin layer (e.g., 5 to 50 angstroms) of refractory metal nitride is provided over a dielectric and oxygen annealed. Preferably, the oxygen anneal is provided by exposing the refractory metal nitride to an oxidizing gas such as oxygen, ozone, or nitrous oxide.